Alignment of Semiconducting Nanowires on Metal Electrodes

ABSTRACT

The present invention relates to a method for aligning semiconducting nanowires on a metal electrode ( 12 ), more particularly to a method for aligning semiconducting nanowires on a metal electrode ( 12 ) by which a zinc oxide nanowire and a silicon nanowire are synthesized on a specific region of an electrode made of Al, Ti, Pt, etc. and the nanowires are aligned on the wafer scale instantly as they are synthesized. The method for aligning semiconducting nanowires on a metal electrode ( 12 ) in accordance with the present invention makes it possible to manufacture multiple nanowire devices at low cost. Thus, the method in accordance with the present invention can be effectively utilized to produce various nano devices, including electronic devices, optoelectronic devices, laser devices, chemical sensors, etc. in large quantity.

TECHNICAL FIELD

The present invention relates to a method for aligning semiconductingnanowires on a metal electrode, more particularly to a method foraligning semiconducting nanowires on a metal electrode by which a zincoxide nanowire and a silicon nanowire are synthesized on a specificregion of an electrode made of Al, Ti, Pt, etc. and the nanowires arealigned on the wafer scale instantly as they are synthesized.

BACKGROUND ART

With the recent advance in semiconductor techniques, electronic devicesare becoming more and more integrated.

Especially, in the field of ultra large-scale integrated circuitsincluding CMOS, etc., the line width of the devices is becoming smallerwith the high-level integration.

As the size of devices becomes small, the importance of the nanowiresthat electrically connect them has been increasingly emphasized.

The nanowires find a multitude of applications in the field of optics,mechanics, electronics, etc.

In general, the nanowires are made of GaAs, GaN, InP, ZnO, etc. andresearches are actively carried out on their use such as alight-emitting device.

Particularly, GaN, GaAs, ZnO, etc. are used to develop bluelight-emitting devices. And, InAs and InP are utilized in the region of1.3 to 1.5 mm.

Because of the advantageous features attained within nano size range andsuperior crystallinity, the nanowires can be utilized in a variety ofelectronic devices, opto-electronic devices, sensors, etc.

The semiconducting nanowire that has been researched most is zinc oxide(ZnO) nanowire. One-dimensional nanoscale objects with a variety offorms (nanowire, nanorod, nanosheet, etc.) have been synthesized bycarbothermal reduction method, chemical vapor deposition (CVD), wetchemical method, pulsed laser deposition (PLD), etc. and theirapplicability for use as optoelectronic devices, laser devices, chemicalsensors, etc. have been identified.

Silicon nanowire can be used in various electronic devices. Typically,silicon nanowire is synthesized by chemical vapor deposition using agold catalyst and a certain precursor vapor phase source (e.g., silanegas).

However, with the utilization of nanowire devices in the semiconductorfield, as compared with the conventional thin film-based technology, thealignment of the nanowires has been raised as a major obstacle.

In the conventional method, after each nanowire is synthesized, anindependent process such as electron beam lithography must be performed.Then, electrodes are adhered thereto to obtain an operable device.

This process, undesirably, is complicated and expensive and thus notsuitable for mass production at low cost.

Accordingly, an object of the present invention is to solve this problemand provide a method for aligning semiconducting nanowires on a metalelectrode by which a zinc oxide nanowire and a silicon nanowire aresynthesized on a specifically defined region of an electrode made ofaluminum, titanium, platinum, etc. and the nanowires are aligned on thewafer scale instantly as they are synthesized. In accordance with thepresent invention, it is possible to manufacture multiple nanowiredevices at once at low cost. Thus, the method in accordance with thepresent invention can be effectively utilized to produce various nanodevices, including electronic devices, optoelectronic devices, laserdevices, chemical sensors, etc., in large quantity.

DISCLOSURE

Hereunder is given a detailed description of the present invention.

The method for aligning semiconducting nanowires on a metal electrode inaccordance with the present invention comprises:

a first step of patterning a gold catalyst layer on a conductingelectrode made of aluminum (Al), titanium (Ti) and platinum (Pt); and

a second step of synthesizing a zinc oxide nanowire and a siliconnanowire in the region where the gold catalyst layer is patterned, asthe nanowires are aligned at the same time.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the devices regularly aligned on a wafer and thenanowires that have grown with patterns as aligned on a conductingelectrode in accordance with the present invention.

FIG. 2 illustrates the process of patterning a conducting electrode anda gold catalyst layer using a mask in accordance with the presentinvention.

FIG. 3 shows the metals that help the growth of the zinc oxide (ZnO)nanowire and the silicon (Si) nanowire depending on the composition ofthe reaction gas and the reaction temperature in accordance with thepresent invention.

FIG. 4 shows that the zinc oxide (ZnO) nanowire grows only on the goldcatalyst, not on a conductive electrode made of aluminum in accordancewith the present invention.

FIG. 5 shows that the silicon (Si) nanowire grows only on the goldcatalyst, not on a conductive electrode made of titanium in accordancewith the present invention.

FIG. 6 shows that the zinc oxide nanowire grows both on a conductiveelectrode made of platinum in accordance with the present invention andthe gold catalyst.

BEST MODE

Now, the present invention is described in more detail referring to theaccompanying drawings.

FIG. 1 illustrates the devices regularly aligned on a wafer and thenanowires that have grown with patterns as aligned on a conductingelectrode in accordance with the present invention.

FIG. 2 illustrates the process of patterning a conducting electrode anda gold catalyst layer using a mask in accordance with the presentinvention.

In a preferred embodiment of the present invention, a conductingelectrode (11) made of aluminum (Al), titanium (Ti), platinum (Pt), etc.is used on a semiconductor wafer (10), as illustrated in FIG. 1.

A gold catalyst layer (12) is patterned on the conducting electrode(11). First, the conducting electrode (11) is processed to a thicknessof 3000-8000 Å and a line width of 100 μm by RF sputtering using ashadow mask (20), as illustrated in FIG. 2.

Typically, the patterning by the RF sputtering is performed under thecondition of 30-80 W, argon (Ar) atmosphere and 10-20 mTorr.

A gold catalyst layer (12) is formed on the resultant conductingelectrode (11). The gold catalyst layer (12) is selectively patterned sothat nanowires may grow only on the specific region of the conductingelectrode (Al, Ti, Pt) (11).

It is well known by those skilled in the art that, when gold is used inthe catalyst layer (12), nanowires may grow as aligned on the desiredsite of the zinc oxide (ZnO) and silicon (Si) substrate.

It is because the source material reacts with the gold catalyst to forma eutectic alloy by the vapor-liquid-solid (VLS) mechanism.

In the present invention, the gold catalyst layer (12) is patterned to athickness of 20-100 Å by ion sputtering.

Nanowires are synthesized after the gold catalyst layer (12) has beenpatterned on the conducting electrode (11) to a desired thickness by ionsputtering. A zinc oxide nanowire is synthesized by the carbothermalreduction method.

Zinc oxide and graphite powder (99.9%; ˜325 mesh; 1:1 mixture) are usedas a source material. The reaction is performed at 800-1000° C. for1-120 minutes.

If the reaction temperature is below 800° C., the eutectic alloy of thesource material and the gold catalyst is not formed easily. In contrast,if the reaction temperature is above 1000° C., a 3D, rather than 1D,nanowire in the form of a large plate is obtained. If the reaction timeis outside the above range, a 1D nanowire is not synthesized well or a3D, rather than 1D, nanowire in the form of a large plate is obtained.

Argon (10-200 sccm) is used as a carrier gas and oxygen (0.1-10 sccm) isinjected as a reaction gas.

If the flow rate of the argon gas is smaller than 10 sccm, the sourcematerial is not fully vaporized, thus causing difficulty in nanowiresynthesis. Also, a flow rate larger than 200 sccm makes the nanowiresynthesis difficult. If the flow rate of the reaction gas oxygen isoutside the above range, a 1D nanowire is not synthesized well or a 3D,rather than 1D, nanowire in the form of a large plate is obtained.

Further, a silicon nanowire is synthesized by the chemical vapordeposition using a silane gas.

At a pressure of 1-100 Torr, a silane (SiH₄) gas and a hydrogen (H₂) gasdiluted to 5% are injected to a metal-organic gas helium (He) at a flowrate of about 10-100 sccm and 10-200 sccm, respectively.

If the reaction pressure is outside the above range, the siliconnanowire is not synthesized properly. If the flow rate of the silane gasand the hydrogen gas is outside the above range, it is difficult toobtain a 1D nanowire or an amorphous SiO₂ nanowire is obtained.

The metals that can give rise to zinc oxide and silicon nanowires underspecific composition and reaction temperature are illustrated in FIG. 3.

That is, FIG. 3 shows the metals that help the growth of the zinc oxide(ZnO) nanowire and the silicon (Si) nanowire depending on thecomposition of the reaction gas and the reaction temperature.

For example, if the ratio of silane (SiH₄)/hydrogen (H₂) of the reactiongas is 10-80 and the reaction temperature is 500-600° C., the siliconnanowire grows only on gold (Au). If the ratio of silane (SiH₄)/hydrogen(H₂) of the reaction gas is 70-120 and the reaction temperature is550-700° C., the silicon nanowire grows only on aluminum (Al). If theratio of silane (SiH₄)/hydrogen (H₂) of the reaction gas is 10-100 andthe reaction temperature is 600-750° C., the silicon nanowire grows ongold (Au) and platinum (Pt). If the ratio of silane (SiH₄)/hydrogen (H₂)of the reaction gas is 20-120 and the reaction temperature is 750-950°C., the silicon nanowire grows on platinum (Pt).

Also, if the ratio of oxygen/argon of the reaction gas is 0.5-12 and thereaction temperature is about 800-850° C., the zinc oxide nanowire growsonly on gold (Au). If the ratio of oxygen/argon of the reaction gas is1-10 and the reaction temperature is about 850-950° C., the zinc oxidenanowire grows on platinum (Pt) and gold (Au). And, if the ratio ofoxygen/argon of the reaction gas is 2-12 and the reaction temperature isabout 950-1000° C., the zinc oxide nanowire grows only on platinum (Pt).

The reason of elucidating the growth of the zinc oxide nanowire and thesilicon nanowire on different metals depending on the composition andreaction gas is stated as follows: the eutectic temperature and theeutectic composition change when the source elements zinc (Zn) andsilicon (Si) of the nanowires are mixed with the platinum (Pt), aluminum(Al) and titanium (Ti) metals of the conducting electrode (11), as shownin Table 1 below.

For example, because the eutectic temperature of zinc (Zn) and gold (Au)is 683° C., the zinc oxide nanowire can be synthesized on gold (Au)within a broad temperature range of 800-950° C. But, the nanowire ishardly synthesized on aluminum (Al) or titanium (Ti) as the Al₂O₃ andTiO₂ oxides are formed.

In case of the silicon nanowire, the inside of the reactor is understrong reduction atmosphere because the hydrogen (H₂) gas is injected,differently from the case of zinc oxide nanowire.

Therefore, the formation of Al₂O₃ or TiO₂ oxides is prevented and thesilicon nanowire can be synthesized on aluminum (Al).

As for titanium (Ti), the synthesis of the silicon nanowire is verydifficult because the eutectic temperature of silicon (Si) and titanium(Ti) is very high at no less than 1300° C.

TABLE 1 Melting point Eutectic Eutectic Alloy (° C.) composition (wt %)temperature (° C.) Al—Zn 660 11:89 381 Ti—Zn 1670 99:01 419 Pt—Zn 1769 —— Au—Zn 1064 85:15 683 Al—Si 660 88:12 577 Ti—Si 1670 92:08 1330  Pt—Si1769 77:23 979 Au—Si 1064 97:03 363

FIG. 4 shows that the zinc oxide (ZnO) nanowire grows only on the goldcatalyst, not on the aluminum conducting electrode (11). The zinc oxidenanowire shown in the figure was obtained by using an aluminum (Al, 5000Å) conducting electrode (11), a part of which is patterned with a goldcatalyst layer (12) (Au, 100 Å) under the synthesis condition C-(7) ofFIG. 3.

As seen in the figure, the zinc oxide nanowire selectively grew only onthe region where the gold catalyst layer (12) was patterned.

FIG. 5 shows that the silicon (Si) nanowire grows only on the goldcatalyst, not on the titanium conducting electrode (11). The siliconnanowire shown in the figure was obtained by using a titanium (Ti, 5000Å) conducting electrode (11), a part of which is patterned with a goldcatalyst layer (12) (Au, 100 Å) under the synthesis condition C-(3) ofFIG. 3.

As seen in the figure, the silicon nanowire selectively grew only on theregion where the gold catalyst layer (12) was patterned.

FIG. 6 shows that the zinc oxide nanowire grows both on the platinumconducting electrode (11) and the gold catalyst. The zinc oxide nanowireshown in the figure was obtained by using a platinum (Pt, 5000 Å)conducting electrode (11), a part of which is patterned with a goldcatalyst layer (12) (Au, 100 Å) under the synthesis condition C-(6) ofFIG. 3.

As seen in the figure, the zinc oxide nanowire grew not only on theregion where the gold catalyst layer (12) was patterned but also on theplatinum electrode (11).

In accordance with the method for aligning semiconducting nanowires on ametal electrode of the present invention, a zinc oxide nanowire and asilicon nanowire are synthesized on a specific region of an electrodemade of aluminum, titanium, platinum, etc. and the nanowires are alignedon the wafer scale instantly as they are synthesized. Accordingly, it ispossible to manufacture multiple nanowire devices at once at low cost.Thus, the method in accordance with the present invention can beeffectively utilized to produce various nano devices, includingelectronic devices, optoelectronic devices, laser devices, chemicalsensors, etc., in large quantity.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the method for aligningsemiconducting nanowires on a metal electrode in accordance with thepresent invention makes it possible to manufacture multiple nanowiredevices at once at low cost. Thus, the method in accordance with thepresent invention can be effectively utilized to produce various nanodevices, including electronic devices, optoelectronic devices, laserdevices, chemical sensors, etc., in large quantity.

Those skilled in the art will appreciate that the concepts and specificembodiments disclosed in the foregoing description may be readilyutilized as a basis for modifying or designing other embodiments forcarrying out the same purposes of the present invention. Those skilledin the art will also appreciate that such equivalent embodiments do notdepart from the spirit and scope of the present invention as set forthin the appended claims.

1. A method for aligning semiconducting nanowires on a metal electrodecomprising: a first step of patterning a gold catalyst layer on aconducting electrode made of aluminum (Al), titanium (Ti) and platinum(Pt); and a second step of synthesizing a zinc oxide nanowire and asilicon nanowire in the region where the gold catalyst layer ispatterned instantly as the nanowires are aligned.
 2. The method foraligning semiconducting nanowires on a metal electrode as set forth inclaim 1, wherein the conducting electrode has a thickness of 3000-8000 Åand a line width of 100 μm.
 3. The method for aligning semiconductingnanowires on a metal electrode as set forth in claim 1, wherein the goldcatalyst layer has a thickness of 20-100 Å and can be patterned by ionsputtering.
 4. The method for aligning semiconducting nanowires on ametal electrode as set forth in claim 1, wherein the zinc oxide nanowireis synthesized by the carbothermal reduction method using zinc oxide andgraphite powder (99.9%; ˜325 mesh; 1:1 mixture) as a source material at800-1000° C. for 1-120 minutes, while injecting argon (10-200 sccm) as acarrier gas and oxygen (0.1-10 sccm) as a reaction gas.
 5. The methodfor aligning semiconducting nanowires on a metal electrode as set forthin claim 1, wherein the silicon nanowire is synthesized by the chemicalvapor deposition under the reaction pressure of 1-100 Torr, whileinjecting a silane (SiH₄) gas and a hydrogen (H₂) gas diluted to 5% areinjected to a metal-organic gas helium (He) at a flow rate of about10-100 sccm and 10-200 sccm, respectively.
 6. The method for aligningsemiconducting nanowires on a metal electrode as set forth in claim 1,wherein the zinc oxide nanowire grows on gold (Au) when the reaction gashas an oxygen/argon ratio of 0.5-12 and the reaction temperature isabout 800-850° C.
 7. The method for aligning semiconducting nanowires ona metal electrode as set forth in claim 1, wherein the zinc oxidenanowire grows on platinum (Pt) and gold (Au) when the reaction gas hasan oxygen/argon ratio of 1-10 and the reaction temperature is about850-950° C.
 8. The method for aligning semiconducting nanowires on ametal electrode as set forth in claim 1, wherein the zinc oxide nanowiregrows on platinum (Pt) when the reaction gas has an oxygen/argon ratioof 2-12 and the reaction temperature is about 950-1000° C.
 9. The methodfor aligning semiconducting nanowires on a metal electrode as set forthin claim 1, wherein the silicon nanowire grows on gold (Au) when thereaction gas has a silane (SiH₄)/hydrogen (H₂) ratio of 10-80 and thereaction temperature is about 500-600° C.
 10. The method for aligningsemiconducting nanowires on a metal electrode as set forth in claim 1,wherein the silicon nanowire grows on aluminum (Al) when the reactiongas has a silane (SiH₄)/hydrogen (H₂) ratio of 70-120 and the reactiontemperature is about 550-700° C.
 11. The method for aligningsemiconducting nanowires on a metal electrode as set forth in claim 1,wherein the silicon nanowire grows on platinum (Pt) and gold (Au) whenthe reaction gas has a silane (SiH₄)/hydrogen (H₂) ratio of 10-100 andthe reaction temperature is about 600-750° C.
 12. The method foraligning semiconducting nanowires on a metal electrode as set forth inclaim 1, wherein the silicon nanowire grows on platinum (Pt) when thereaction gas has a silane (SiH₄)/hydrogen (H₂) ratio of 20-120 and thereaction temperature is about 750-950° C.